From orogeny to rifting: insights from the Norwegian \u2018reactivation phase\u2019

Gwenn Peron-Pinvidic,Per Terje Osmundsen

doi:10.1038/s41598-020-71893-z

Gwenn Peron-Pinvidic, Per Terje Osmundsen

Open Access

https://doi.org/10.1038/s41598-020-71893-z

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Abstract

Based on observations from the Mid-Norwegian extensional system, we describe how, when and where the post-Caledonian continental crust evolved from a context of orogenic disintegration to one of continental rifting. We highlight the importance of a deformation stage that occurred between the collapse mode and the high-angle faulting mode often associated with early rifting of continental crust. This transitional stage, which we interpret to represent the earliest stage of rifting, includes unexpected large magnitudes of crustal thinning facilitated through the reactivation and further development of inherited collapse structures, including detachment faults, shear zones and metamorphic core complexes. The reduction of the already re-equilibrated post-orogenic crust to only ~ 50% of normal thickness over large areas, and considerably less locally, during this stage shows that the common assumption of very moderate extension in the proximal margin domain may not conform to margins that developed on collapsed orogens.

Highlights

Based on observations from the Mid-Norwegian extensional system, we describe how, when and where the post-Caledonian continental crust evolved from a context of orogenic disintegration to one of continental rifting
The resulting structural template commonly involves metamorphic core complexes, extensional shear zones and detachment faults superposed on inherited thrust assemblagesSPS:refid::bib[99]
Based on our observations from seismic reflection data, and on published evidence for reactivation of detachments in East Greenland and Norway, we propose that the transition between extensional collapse and early rifting corresponds to a specific, previously unspecified phase of deformation

Summary

The Norwegian case

Onshore outcrops in western and south-western Norway display major extensional shear zones and detachment faults interpreted as related to the collapse of the Scandinavian Caledonides[14] (Figs. 1, 2, 3). As summarized above, mapping permitted by the modern seismic datasets shows that the offshore Norwegian proximal areas—from the Trøndelag Platform down to the North Sea Stord Basin/Utsira High—are floored by a unit of anastomosing shear zones and metamorphic core complexes, associated with long-lived detachment faults[23,24] These geometries appear extremely different from the geometries normally attributed to the early rifting deformation mode in a number of recent m odels[2]. Based on our observations from seismic reflection data, and on published evidence for reactivation of detachments in East Greenland and Norway, we propose that the transition between extensional collapse and early rifting corresponds to a specific, previously unspecified phase of deformation This ‘reactivation phase’ (Fig. 4) is interpreted as an important stage in the evolution of rifted margins that initiate on previous orogens. The extensional system evolved in a succession of distinct deformation phases, migrating oceanwards, as often assumed in conceptual models[2,12] (Fig. 5)

Conclusions

Additional information